The manufacture of many types of work pieces requires the substantial planarization or polishing of at least one surface of the work piece. Examples of such work pieces that require a planar surface include semiconductor wafers, optical blanks, memory disks, and the like. One commonly used technique for planarizing the surface of a work piece is the chemical mechanical planarization (CMP) process. The terms “planarization” and “polishing,” or other forms of these words, although having different connotations, are often used interchangeably by those of skill in the art with the intended meaning conveyed by the context in which the term is used. For ease of description such common usage will be followed and the term “chemical mechanical planarization” will generally be used herein with that term and “CMP” conveying either “chemical mechanical planarization” or “chemical mechanical polishing.” The terms “planarize” and “polish” will also be used interchangeably.
The CMP method typically requires the work piece to be loaded into and mounted precisely on a carrier head in a manner such that the surface to be planarized is exposed. The exposed side of the work piece is then held against a polishing pad and relative motion is initiated between the work piece surface and the polishing pad in the presence of a polishing slurry. The mechanical abrasion of the surface caused by the relative motion of the work piece with respect to the polishing pad combined with the chemical interaction of the slurry with the material on the work piece surface ideally produces a planar surface.
The polishing slurry can be applied to the surface of the polishing pad by deposition of the slurry directly onto the polishing surface of the polishing pad or, alternatively, the slurry can be delivered from a manifold assembly underlying the polishing pad through supply apertures or “through-holes” within the polishing pad. Spent slurry, that is, slurry that has reacted with the work piece surface and contains by-products from the polishing process then is removed from the surface of the polishing pad so that it can be replaced by fresh slurry for uniform planarization.
As an alternative to traditional CMP, electrochemical mechanical planarization (ECMP) can be used for polishing the work piece. ECMP involves removal of material from the surface of the work piece through the action of an electrolyte solution, electricity, and relative motion between the work piece and the surface of the polishing pad. The ECMP slurry, or electrolyte, also needs to be removed from the surface of the polish pad as does traditional CMP slurry.
Various methods have been used to remove the spent slurry from the polishing pad. One method utilizes polishing pads having grooves within the surface of the polishing pad that permit the spent slurry to flow out from the center of the polishing pad to be exhausted from a peripheral edge of the pad. While wide grooves would permit the slurry to flow freely, the width of the grooves is limited because wider grooves result in less polishing pad available for contact with the work piece. Accordingly, with narrow grooves, the flow of the slurry may be restricted and the residence time of the spent slurry on the surface of the pad may be longer than desired. As a result, a pressure gradient forms across the polishing pad from the center to the peripheral edge. This slurry build-up also may cause the work piece to hydroplane on the polishing pad, decreasing the polishing rate. Moreover, as the polishing pad wears, the depth of the grooves becomes even smaller, thus further reducing the volume of slurry the grooves can carry and compounding the above problems.
Another method for removing slurry from the surface of a polishing pad includes exhaust ports that extend through the polishing pad and the underlying polishing assembly. The polishing assembly can include one or more polishing sub-pads, such as a backing pad, a platen that is configured to support the polishing pad, and a manifold assembly that distributes the slurry to the surface of the polishing pad. The exhaust ports may use the force of gravity to exhaust the slurry or may be connected to a pump that pumps the slurry from the polishing pad. Accordingly, the exhaust ports are configured to extend, not only through the polishing pad, but also any polishing sub-pads, the platen and the manifold assembly. Because the polishing sub-pads, platen, and manifold assembly are manufactured separately, the exit ports add a high degree of complexity to the designing and manufacturing of the polishing pad assemblies.
Accordingly, it is desirable to provide work piece polishing assemblies that provide for the efficient and passive removal of slurry from the surface of a polishing pad of a CMP apparatus. In addition, it is desirable to CMP apparatuses that utilize such work piece polishing assemblies. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.